The present invention relates to a driving circuit for supplying a radio frequency electrical signal to the applicator section of a radio frequency dryer and, more particularly, to a driving circuit which supplies a radio frequency signal at a frequency substantially equal to the resonant frequency of the applicator section.
Radio frequency drying systems are particularly advantageous for drying ink on paper sheets or a paper web. It is, of course, desirable to apply radio frequency power to the dryer applicator section in as efficient a manner as possible. This implies controlling the potential level of the radio frequency signal applied to the applicator section and further requires control of the loading of the power amplifier in the driving circuit. The best efficiency in such a system is obtained if the unloaded Q of the applicator section is as high as possible. If paper bearing very little ink or a great deal of ink passes through the dryer, the resonant frequency, the loading, and the Q of the system will vary substantially. The problem, therefore, is to adjust the frequency of the driving signal so that it equals the resonant frequency of the applicator section and, further, to maintain both a desired amplitude of driving signal and an efficient transfer of the driving signal into the applicator section in the face of widely varying loading.
A need exists for a driving circuit capable of supplying a radio frequency electrical signal to the applicator section of a radio frequency dryer in an efficient, controlled fashion at a predetermined voltage level and at the resonant frequency of the dryer section.